Adatabaseis an organized collection ofdata.[1]It is the collection of tables,queries,reports,views and other objects. The data is typically organized to model aspects of reality in a way that supportsprocessesrequiring information, such as modelling the availability of rooms in hotels in a way that supports finding a hotel with vacancies.Database management systems (DBMS)arecomputer softwareapplications that interact with the user, other applications, and the database itself to capture and analyze data. A general-purpose DBMS is designed to allow the definition, creation, querying, update, and administration of databases. Well-known DBMSs includeMySQL,PostgreSQL,Microsoft SQL Server,Oracle,SybaseandIBM DB2. A database is not generallyportableacross different DBMSs, but different DBMS can interoperate by usingstandardssuch asSQLandODBCorJDBCto allow a single application to work with more than one DBMS. Database management systems are often classified according to thedatabase modelthat they support; the most popular database systems since the 1980s have all supported therelational modelas represented by theSQLlanguage. Sometimes a DBMS is loosely referred to as a 'database'.Data hierarchyrefers to the systematic organization of data, often in a hierarchical form. Data organization involves fields, records, files and so on.[1]Adata fieldholds a single fact or attribute of an entity. Consider a date field, e.g. "September 19, 2004". This can be treated as a single date field (e.g. birthdate), or 3 fields, namely, month, day of month and year.Arecordis a collection of related fields. An Employee record may contain a name field(s), address fields, birthdate field and so on.Afileis a collection of related records. If there are 100 employees, then each employee would have a record (e.g. called Employee Personal Details record) and the collection of 100 such records would constitute a file (in this case, called Employee Personal Details file).Files are integrated into adatabase.[2]This is done using a Database Management System.[3]If there are other facets of employee data that we wish to capture, then other files such as Employee Training History file and Employee Work History file could be created as well.